Design: Population-based registry cohort with record linkage
Population: 5,202 people diagnosed with type 1 diabetes before age 16 in New South Wales
Primary outcome: Chronic complications within 20 years of diagnosis
Effect: Onset <7 vs 13–15 years: severe retinopathy aHR 0.25 (0.17–0.36); kidney aHR 0.40 (0.30–0.53)

Researchers linked a New South Wales registry of 5,202 children diagnosed with type 1 diabetes before 16 years, between 1990 and 2009, to hospital, emergency, insurance and death records up to 2019.

Within 20 years of diagnosis, those diagnosed before age 7 had substantially lower risk of most chronic complications than those diagnosed at 13 to 15 years. Adjusted hazard ratios were 0.16 for peripheral neuropathy, 0.25 for severe retinopathy, 0.32 for cardiac complications and 0.40 for kidney complications. When risk was compared by attained age (16 to 34 years), there was no difference.

The pattern fits the idea that prepubertal years count for less towards complications. It means a young adult diagnosed in their early teens may reach complications by their early thirties, and their surveillance should reflect that.

Note the age at diagnosis in every young adult with type 1 diabetes.
Start retinal, urine albumin and foot screening on schedule in those diagnosed in adolescence.
Do not assume a person in their twenties is too young for complications if onset was at 13 or older.
Use transition clinics to keep adolescent-onset patients from dropping out of follow-up.

Why it matters

Duration alone undercounts risk; the teenage years seem to count more.

The statistics, in plain English

A hazard ratio of 0.25 for severe retinopathy means about a quarter of the rate in the youngest-onset group compared with adolescent onset over the same duration. The confidence intervals all sit well below 1, so the difference is unlikely to be chance, but this is registry data and cannot separate puberty from other differences between the groups.